Commit fdf1cdb9 authored by Johannes Weiner's avatar Johannes Weiner Committed by Linus Torvalds
Browse files

mm: remove unnecessary uses of lock_page_memcg() 



There are several users that nest lock_page_memcg() inside lock_page()
to prevent page->mem_cgroup from changing.  But the page lock prevents
pages from moving between cgroups, so that is unnecessary overhead.

Remove lock_page_memcg() in contexts with locked contexts and fix the
debug code in the page stat functions to be okay with the page lock.

Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Acked-by: default avatarVladimir Davydov <vdavydov@virtuozzo.com>
Cc: Michal Hocko <mhocko@suse.cz>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 62cccb8c

include/linux/memcontrol.h

+7 −5
Original line number Diff line number Diff line
@@ -28,6 +28,7 @@ 
#include <linux/eventfd.h>

#include <linux/mmzone.h>

#include <linux/writeback.h>

#include <linux/page-flags.h>



struct mem_cgroup;

struct page;
@@ -464,18 +465,19 @@ void unlock_page_memcg(struct page *page); 
 * @idx: page state item to account

 * @val: number of pages (positive or negative)

 *

 * Callers must use lock_page_memcg() to prevent double accounting

 * when the page is concurrently being moved to another memcg:

 * The @page must be locked or the caller must use lock_page_memcg()

 * to prevent double accounting when the page is concurrently being

 * moved to another memcg:

 *

 *   lock_page_memcg(page);

 *   lock_page(page) or lock_page_memcg(page)

 *   if (TestClearPageState(page))

 *     mem_cgroup_update_page_stat(page, state, -1);

 *   unlock_page_memcg(page);

 *   unlock_page(page) or unlock_page_memcg(page)

 */

static inline void mem_cgroup_update_page_stat(struct page *page,

				 enum mem_cgroup_stat_index idx, int val)

{

	VM_BUG_ON(!rcu_read_lock_held());

	VM_BUG_ON(!(rcu_read_lock_held() || PageLocked(page)));



	if (page->mem_cgroup)

		this_cpu_add(page->mem_cgroup->stat->count[idx], val);

mm/filemap.c

+1 −6
Original line number Diff line number Diff line
@@ -176,8 +176,7 @@ static void page_cache_tree_delete(struct address_space *mapping, 
/*

 * Delete a page from the page cache and free it. Caller has to make

 * sure the page is locked and that nobody else uses it - or that usage

 * is safe.  The caller must hold the mapping's tree_lock and

 * lock_page_memcg().

 * is safe.  The caller must hold the mapping's tree_lock.

 */

void __delete_from_page_cache(struct page *page, void *shadow)

{
@@ -260,11 +259,9 @@ void delete_from_page_cache(struct page *page) 


	freepage = mapping->a_ops->freepage;



	lock_page_memcg(page);

	spin_lock_irqsave(&mapping->tree_lock, flags);

	__delete_from_page_cache(page, NULL);

	spin_unlock_irqrestore(&mapping->tree_lock, flags);

	unlock_page_memcg(page);



	if (freepage)

		freepage(page);
@@ -557,7 +554,6 @@ int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask) 
		new->mapping = mapping;

		new->index = offset;



		lock_page_memcg(old);

		spin_lock_irqsave(&mapping->tree_lock, flags);

		__delete_from_page_cache(old, NULL);

		error = radix_tree_insert(&mapping->page_tree, offset, new);
@@ -572,7 +568,6 @@ int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask) 
		if (PageSwapBacked(new))

			__inc_zone_page_state(new, NR_SHMEM);

		spin_unlock_irqrestore(&mapping->tree_lock, flags);

		unlock_page_memcg(old);

		mem_cgroup_migrate(old, new);

		radix_tree_preload_end();

		if (freepage)

mm/page-writeback.c

+0 −2
Original line number Diff line number Diff line
@@ -2700,7 +2700,6 @@ int clear_page_dirty_for_io(struct page *page) 
		 * always locked coming in here, so we get the desired

		 * exclusion.

		 */

		lock_page_memcg(page);

		wb = unlocked_inode_to_wb_begin(inode, &locked);

		if (TestClearPageDirty(page)) {

			mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_DIRTY);
@@ -2709,7 +2708,6 @@ int clear_page_dirty_for_io(struct page *page) 
			ret = 1;

		}

		unlocked_inode_to_wb_end(inode, locked);

		unlock_page_memcg(page);

		return ret;

	}

	return TestClearPageDirty(page);

mm/truncate.c

+0 −3
Original line number Diff line number Diff line
@@ -527,7 +527,6 @@ invalidate_complete_page2(struct address_space *mapping, struct page *page) 
	if (page_has_private(page) && !try_to_release_page(page, GFP_KERNEL))

		return 0;



	lock_page_memcg(page);

	spin_lock_irqsave(&mapping->tree_lock, flags);

	if (PageDirty(page))

		goto failed;
@@ -535,7 +534,6 @@ invalidate_complete_page2(struct address_space *mapping, struct page *page) 
	BUG_ON(page_has_private(page));

	__delete_from_page_cache(page, NULL);

	spin_unlock_irqrestore(&mapping->tree_lock, flags);

	unlock_page_memcg(page);



	if (mapping->a_ops->freepage)

		mapping->a_ops->freepage(page);
@@ -544,7 +542,6 @@ invalidate_complete_page2(struct address_space *mapping, struct page *page) 
	return 1;

failed:

	spin_unlock_irqrestore(&mapping->tree_lock, flags);

	unlock_page_memcg(page);

	return 0;

}

mm/vmscan.c

+0 −4
Original line number Diff line number Diff line
@@ -607,7 +607,6 @@ static int __remove_mapping(struct address_space *mapping, struct page *page, 
	BUG_ON(!PageLocked(page));

	BUG_ON(mapping != page_mapping(page));



	lock_page_memcg(page);

	spin_lock_irqsave(&mapping->tree_lock, flags);

	/*

	 * The non racy check for a busy page.
@@ -647,7 +646,6 @@ static int __remove_mapping(struct address_space *mapping, struct page *page, 
		mem_cgroup_swapout(page, swap);

		__delete_from_swap_cache(page);

		spin_unlock_irqrestore(&mapping->tree_lock, flags);

		unlock_page_memcg(page);

		swapcache_free(swap);

	} else {

		void (*freepage)(struct page *);
@@ -675,7 +673,6 @@ static int __remove_mapping(struct address_space *mapping, struct page *page, 
			shadow = workingset_eviction(mapping, page);

		__delete_from_page_cache(page, shadow);

		spin_unlock_irqrestore(&mapping->tree_lock, flags);

		unlock_page_memcg(page);



		if (freepage != NULL)

			freepage(page);
@@ -685,7 +682,6 @@ static int __remove_mapping(struct address_space *mapping, struct page *page, 


cannot_free:

	spin_unlock_irqrestore(&mapping->tree_lock, flags);

	unlock_page_memcg(page);

	return 0;

}

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